Interpretive Summary: Sclerotinia sclerotiorum can cause serious yield losses in oilseed crops in the United States and worldwide. Chemical control measures for diseases caused by this pathogen are often ineffective and can be hazardous to man and the environment. Other control measures such as plant breeding have met with limited success. Biological control measures for these diseases need to be developed due to environmental problems associated with existing chemical controls and the limited effectiveness of other traditional control measures. In this study we show that two different formulations of oilseed rape seed containing the beneficial bacterium Bacillus subtilis Tu-100 significantly suppressed disease caused by S. sclerotiorum on oilseed rape in field trials conducted at two locations that differed in soil type. Oilseed rape seed yield was significantly increased in treatments containing this bacterium in one of the two locations. It was also shown that both of these formulations have good shelf-life, a property necessary for commercialization of biological control agents. Experiments reported here identify the antibiotic iturin as being produced by this bacterium. This information will be useful to scientists devising strategies for biological control of diseases on oilseed crops caused by S. sclerotiorum.

Technical Abstract:
Sclerotinia sclerotiorum causes serious yield losses in crops in The People’s Republic of China. Two formulations of oilseed rape seed containing the endophytic bacterium Bacillus subtilis Tu-100 were evaluated for suppression of this pathogen in field trials conducted at two independent locations. The pellet formulation significantly reduced disease (incidence and disease index) and increased plant dry weight while the wrap formulation significantly reduced disease incidence and significantly increased plant dry weight at both field locations. Mean seed yield per 120 plants with both formulations of isolate Tu-100 was significantly greater than the appropriated controls, but at only one of the locations. Both formulations provided stable B. subtilis Tu-100 biomass (> 10 5 CFU) and seed germination (> 85%) over a six month period at room temperature. Polymerase chain reaction and DNA sequence analysis identified ituC and ituD, and bacAB and bacD in the genome of isolate Tu-100. These genes are involved in the biosynthesis of iturin and bacilysin. Iturin was detected in culture filtrates from isolate Tu-100 with thin layer chromatography. Detection of bacilysin was not attempted. Experiments reported here indicate the commercial viability of B. subtilis Tu-100 for suppression of S. sclerotiorum on oilseed rape and suggest a mechanism for suppression.